This invention relates to compositions that are useful as plasticizers for polyvinylchloride (commonly referred to as PVC). More particularly, it relates to plasticizers for PVC intended for use in high temperature resistant applications.
Trimellitate esters, such as tri(2-ethylhexyl)trimellitate, are known plasticizers for PVC for many uses where plasticizing efficiency, permanence, and physical property retention are important, such as high temperature resistant wire and cable jacketing and insulation, as well as other high temperature applications.
Extenders (often called secondary plasticizers), normally incompatible with PVC, are often used in combination with certain plasticizers for PVC to reduce costs, extend plasticizers in short supply. The extendability of a given plasticizer depends upon its ability to compatibilize compounds that would be useful as secondary plasticizers for PVC.
The values for the solubility parameter and the dielectric constant of a plasticizer are theorized to be good indicators of the compatibility of the plasticizer with PVC and also are indicators of whether or not a plasticizer can be extended with a secondary plasticizer, which usually is only marginally compatible with PVC. Stated in other words, the values indicate the ability of a plasticizer to compatibilize an extender or secondary plasticizer. In general, the closer the value of the solubility parameter is to 9.9, and the closer the dielectric constant is to between 6 and 7, the better will that plasticizer be in compatibilizing secondary plasticizers or extenders (see J. K. Sears and J. R. Darby, "The Technology of Plasticizers", John Wiley and Sons, Inc., 1982, pp 484-486).
To be practically useful for high temperature resistant PVC applications, an extender for trimellitate esters, such as for example, tri(2-ethylhexyl)trimellitate, must have sufficient plasticizing efficiency (i.e., impart good physical properties) and high temperature permanence (i.e., maintain good physical properties under high temperature stress) as well as be compatibilized by the trimellitate ester. However, based on the above theory, since tri(2-ethylhexyl)trimellitate has a solubility parameter (9.0) indicating only marginal compatibilizing power and a dielectric constant (4.7) indicating poor compatibilizing power, an extender that would be practically useful for trimellitate esters, such as tri(2-ethylhexyl)trimellitate, used to plasticize PVC intended for use in high temperature resistant applications would be unexpected, and until now, was unknown.